Ceramic Veneers Preparation Guide

Veneers a re p artia l e xtr a co ro na l r e sto ra tio ns u su ally in dic a te d fo r a nte rio r esth etic r e habilit a tio n s. T he m ain p urp o se o f a v e neer is to c o ve r th e la bia l- p ro xim al s u rfa ce s a nd p ote ntia lly th e in cis a l b ord e r o f th e...

Veneers a re p artia l e xtr a co ro na l r e sto ra tio ns u su ally in dic a te d fo r a nte rio r esth etic r e habilit a tio n s. T he m ain p urp o se o f a v e neer is to c o ve r th e la bia l- p ro xim al s u rfa ce s a nd p ote ntia lly th e in cis a l b ord e r o f th e a nte rio r te eth in a n a tte m pt to c o rre ct c o lo r d is cre p ancie s, s h ape, te xtu re , fu nctio n, and p osit io n o f th e e le m en ts in th e d enta l a rc h . T here a re s e ve ra l pre para tio n d esig ns fo r c e ra m ic v e neers , w hic h v a ry a cco rd in g to th e exte nt o f th e p re para tio n. T he u se o f d if fe re n t p re p ara tio n te ch niq ues is dependent o n s e ve ra l fa cto rs : th e a m ou nt o f r e m ain in g to oth s tr u ctu re , pre se nce o f p re vio us r e sto ra tio ns, le ngth o f th e c lin ic a l c ro w n, a nd pre se nce o f e ndodon tic t r e atm ent. Pre para tio ns fo r la m in ate v e n eers d o, in fa ct, r e q uir e g re a t s tr in gency a nd a g re at d eal o f tr a in in g , a s n o r e ctif ic a tio n c a n b e m ad e o nce th e p ro ce dure is c o m ple te d. E xp erie nce is r e quir e d fo r m aste ry o f 0 .3 -0 .5 m m r e ductio ns. Enam el ​Vs ​Den tin Tooth p re para tio n fo r th e la m in a te v e neers is e xa ctin g. U sin g m agnif ic a tio n lo upes to fa cilit a te c a re fu l p re para tio n is tr e m en dously h elp fu l fo r acco m plis h in g th is s te p. It a ls o h elp s to p re se rv e a s m uch e nam el a s possib le a s th e b ond s tr e ng th o f p orc e la in b onded to e nam el is s till s u perio r when c o m pare d w it h th e b ond s tr e n gth o f p orc e la in b onded to d entin . The m ore th e b o ndin g s u rfa ce s w ere lo ca te d in d entin , th e lo w er th e s u cce ss r a te .. This c o uld b e e xp la in ed b y th e d if fe re n ce in th e e la stic m odulu s b etw een th e s u bstr a te a nd th e c e ra m ic . T he lo w er th is r a tio , th e b ette r th e fr a ctu re re sis ta nce . T his e xp la in s w hy b ondin g to e nam el ( 7 0 G Pa) is p re fe ra ble to dentin ( 1 8 G Pa) b eca use th e d if fe re n ce in th e e la stic m od ulu s is lo w er w it h ce ra m ic ( b etw een 6 5 G Pa fo r f e ld sp ath ic a nd 9 5 G Pa fo r IP S e .m ax). To e nsu re th e b ond s tr e n gth o f th e r e sin c o m po sit e to th e to oth s u rfa ce it is nece ssa ry to r e duce th e e na m el. D ue to it s p oor r e te ntio n c a pacit y , th e apris m atic to p s u rfa ce o f m atu re te eth th at h ave n ot b een p re p are d m ust be r e m ove d, o r a t le ast r o ughe ned. C are fu l a tte ntio n is o f th e u tm ost im porta nce in o rd er t o o b ta in s u cce ssfu l r e su lt s a nd s o lid b ondin g. How eve r, R ig id it y in th e to oth is d ue to th e a m ou nt o f e nam el th ic kn ess, and th us, The m ore e nam el th at is r e m ove d , th e m ore th e to oth fle xe s. As th e a nato m y a nd t h e s h ade o f th e r e sto ra tio n a re d ir e ctly a ffe cte d b y th e pre para tio n d esig n, v e ry p re cis e p la nnin g is n ece ssa ry . T he c e ra m ic mate ria l a llo w s fo r th e r e p ro d uctio n o f n atu ra l lig ht tr a n sm is sio n ( i. e . re fr a ctio n, r e fle ctio n, tr a n slu ce n cy) a nd a n e sth etic r e su lt c a n b e h in dere d by in su ffic ie nt to oth p re p ara tio n in r e la tio n to th e s o ft tis su e p ara m ete rs a nd th e r e sto ra tio n. 1 Enam el r e m oval The s h ape o f th e p re para tio ns a ls o in flu ence s th e a ppeara n ce a nd lo ngevit y o f a r e sto ra tio n. In o rd er to m an ip ula te lig ht a nd to e sta blis h a depth o f tr a nslu ce ncy a nd s p ace fo r th e in cis a l e ffe cts is d esir e d . Wit h out r e ductio n, th e te eth w il l b e la rg e r a nd m ore la bia lly p osit io ned ( in lin gually in clin ed te eth , th is m ay b e a n a dva nta ge). F ailu re to r e m ove pro xim al e nam el c a n r e su lt in t h e fin is h lin e p la ce d to o fa r la bia lly a nd encro ach m ent o n th e e m bra su re a re a s, r e su lt in g in e xp osu re o f u nsig htly porc e la in m arg in s th a t m ay b e d if fic u lt to fin is h . P ro ce edin g w it h out pre para tio n w ill le ad to n ot o nly d is tin ct o ve rc o n to urin g a t c e rv ic a l a nd pro xim al to oth s u rfa ce s, b u t a ls o to h ig her c lin ic a l fa ilu re r a te s a s a r e su lt o f gin giv a l in fla m matio n a nd s e co n dary c a rie s d ue to a n in cre a se in m ic ro bia l pla que a ccu m ula tio n. The c o ntin uin g e vo lu tio n o f b ond in g p ro ce sse s to d enta l s tr u ctu re s m ake s possib le th e im ple m enta tio n o f m ore c o nse rv a tiv e r e sto ra tiv e te ch niq ues and e nable s th e u se o f m in im ally in va siv e p re p ara tio ns. In te eth w it h s lig ht o r n o d is co lo ra tio n, fo r e xa m ple , c e ra m ic v e neers w it h th ic kn esse s r a ngin g fr o m 0 .3 to 0 .7 m m m ay b e u se d. E xtr e m ely th in ce ra m ic v e neers e m erg ed , r e quir in g m in im al to oth r e d uctio n th at is lim it e d to m ere ly s m ooth in g s h arp a ngle s a nd e lim in atin g u nderc u ts . T eeth in dic a te d to r e ce iv e th is ty p e o f r e sto ra tio n u su ally h ave fa vo ra b le ch ara cte ris tic s s u ch a s a g ood in se rtio n a xis a nd a dequate s p ace fo r th e re sto ra tio n. T hese p re para tio n s h ave v e ry s p ecif ic in dic a tio ns, w here re sh apin g o r c o rre ctio n o f to oth v o lu m e is n ece ssa ry b y a ddin g m ate ria l. NB. It s h ould b e n ote d th at c e ra m ic v e neers a re o f lim it e d u se in s it u atio ns re quir in g m ajo r c o rr e ctio n . 2 When t o c o nsid er r e d u ctio n ? 1. Rem ove c o nve xit ie s a nd p ro vid e a p ath fo r in se rtio n in th ose sit u atio ns w here e it h er th e in cis a l o r th e in te rp ro xim al a re a s a re to b e in clu ded in th e v e neer. 2. Pro vid e s p ace fo r a d equa te o paqu in g o r h eavie r c o lo rin g lik e in c a se s of a d ark s u bstr a te . 3. Pro vid e a d efin it e s e a t to h elp to p osit io n th e v e neer d urin g pla ce m ent. 4. Pre pare a r e ce ptiv e e n am el s u rfa ce fo r e tc h in g a nd b ondin g th e ve neer. 5. Allo w fo r a s m ooth er tr a nsit io n fr o m th e v e neer to th e to oth s u rfa ce , enablin g th e p a tie nt to m ore e asily k e ep it p la que - fr e e . Contr a in dic atio ns t o r e d uctio n: 1. The s iz e o f th e p u lp . If y o un g in div id uals o r o th ers w it h la rg e p ulp s re quir e la m in atin g, c o nsid e r a n a lt e rn a tiv e to e nam el r e ductio n, esp ecia lly if th ere is a ny in d ic a tio n o f ir re ve rs ib le s e nsit iv it y b y re ducin g th e th ic kn ess o f th e e nam el. 2. The p atie nt’s p sych o lo gic a l s ta te a nd fe elin gs a bout to oth r e ductio n or v e neers . If t h e p atie nt is a pp re h ensiv e a nd u nsu re , th en it is w is e to d o n o r e ductio n . T hen if th e p atie nt b eco m es d is sa tis fie d w it h th e ve neer o r th e s lig htly o ve rb u ilt lo ok, th e o ptio n w ill b e r e m ovin g th e porc e la in v e nee r a nd r e po lis h in g th e e nam el, th us r e tu rn in g th e patie nt to a s e m bla n ce o f t h e ir p re - ve neer s ta te . If r e d ucin g,, h ow m uch ? As a g enera l p rin cip le , t h e e nam el s h ould b e r e d uce d ju st a s m uch a s nece ssa ry to fa cilit a te th e p la ce m ent o f a n e sth etic r e sto ra tio n. Id eally , o ne would lik e to r e m ove t h e s a m e a m ou nt o f e nam el th at w ill e ve ntu ally b e re pla ce d b y th e v e n eer a nd b o ndin g c o m po sit e r e sin . D ecis io ns a bout re ductio n n eed to ta ke in to a cco u nt th e r e la tiv e p osit io n o f th e to oth in th e 3 arc h . F or e xa m ple , in t r e atin g a c ro w ded o r r o ta te d to oth o r a to oth in a la bia l v e rs io n, it m ay b e a dva nta g eous to fir s t b rin g th e o ffe ndin g to oth in to alig nm ent w it h th e r e st o f th e a rc h b y r e d ucin g it s la bia l c o nto ur th ro ugh co sm etic c o nto urin g. T hu s, T he u se o f m ock - ups, fo llo w ed b y a w ax m odel, esth etic p re - eva lu ativ e te m pora rie s, a nd s ilic o ne in dex, p ro vid es th e b est esth etic , p honetic , a n d fu nctio n al a sse ssm en t o f n ece ssa ry to oth pre para tio n fo r v e neers . 4 Ven eers p re p ara tio ns Pre para tio ns fo r c e ra m ic v e n eers h ave u nderg o ne m any c h anges a nd adva nce s. T he p re para tio n s h ape c a n b e in flu ence d b y to oth s h ape, lo ca tio n a nd o rie nta tio n in th e a rc h , to oth a nato m y, o cclu sa l fu nctio n, mech anic a l fo rc e s, q ua ntit y a nd q ualit y o f th e r e m ain in g to oth s tr u ctu re a nd antic ip ate d fin al r e sto ra tiv e d im ensio n. B y u sin g th ese c lin ic a l co nsid era tio ns, m odif ic a tio n s in th e p re p ara tio n s h apes m ay b e v a rie d a nd fin d a m ult it u de o f s h ap es, b ein g g uid ed b y th e p re -e xis tin g d efe ct o r dependin g o n th e a ntic ip ate d d im en sio n o f th e fin al r e sto ra tio n a nd th e su bstr a te s h ade. 5 The g oals o f p re p ara tio n : ● To c re ate e nou gh s p ace f o r th e c e ra m ic m ate ria l ● To m ain ta in a s m uch e n am el a s p ossib le . ● A d efin it e fin is h li n e fo r th e te ch n ic ia n. ● A s m ooth p re p ara tio n w it h out s h arp lin e a ngle s. 6 No prep This c o nce pt h as b eco m e v e ry p opula r in r e ce nt y e ars d ue to it s co m merc ia l a ttr a ctiv e ness fo r p atie nts . H ow eve r, it is im po rta nt to h ig hlig ht th e m any lim it a tio ns; e sth etic a lly ( o ve rh a ngs) a nd in te rm s o f it s a pplic a tio n in th e la bora to ry ( u lt r a -th in v e n eers ) a nd in th e c lin ic ( e xtr e m ely d elic a te to bond). V ery fe w c lin ic a l s it u atio ns a re in fa ct e lig ib le fo r th is p ure ly a ddit iv e co nce pt. Rece ntly , in te rd is cip li n ary c a re w as a p illa r o f th is e vo lu tio n b y fu lly in clu din g o rth odontic s in th e tr e atm en t p la ns. T he o rth odontic m ove m ent would c re ate th e n e ce ssa ry th ic kn ess ( 0 .5 m m) fo r th e fin al r e sto ra tio ns. A s a r e su lt , th e c lin ic ia n o nly h a d to d ra w th e c o nto urs o f th e p re para tio n wit h out h avin g to r e d uce th e th ic kn ess o f th e to oth u nnece ssa rily . T his prin cip le m ust a cco rd in g to lo gic , fo llo w th e fin al e sth etic p la n th at w as esta blis h ed a t th e b eg in nin g o f th e tr e a tm en t. T he p osit io nin g s o ught b y th e orth odontic a ctio n m ust b e c o n tr o lle d a nd th e o cclu sa l k e y b ase d o n th e wax-u p s h ould v a lid ate th e o bta in ed s p ace . T hus, it is s till s o m e s o rt o f debate a nd c a n n ot b e a ppli e d to a ll c a se s b ut n eeds p re cis e c a se se le ctio n. 7 It is w orth r e m em berin g th at th e fin al o bje ctiv e a nd th e th ic kn ess o f th e re sto ra tiv e m ate ria l s h ou ld b e c o n sid ere d to a vo id o ve rc o nto urin g o f th e re sto re d te eth . A noth er c o nsid e ra tio n is th e a m ou nt o f m askin g r e quir e d o n th e d enta l s tr u ctu re . S eve ra l d is co lo ra tio ns c o uld r e q uir e a c o nsid era ble th ic kn ess o f r e sto ra tiv e m ate ria l a nd a s a r e su lt , a m ore in va siv e to oth pre para tio n r e su lt a nd t o d e te rm in e th e fin al th ic kn ess a nd m orp holo gy o f th e to oth a nd o f th e r e sto ra tio n. Som e o f th e ​adva nta ges ​of t h is c o nce pt in r e la tio n to c o nve ntio nal v e neers (w it h p re para tio n) a re : ● pre se rv a tio n o f s o und t o o th s tr u ctu re ● re duce d c lin ic a l t im e fo r th e im pre ssio n-ta kin g s te p ● elim in atio n o f th e p ro vis io n al s te p ● bondin g e xclu siv e ly t o th e e n am el. Dis a dva nta ges ​ a re : ● th e m etic u lo us a n d th oro ugh m anufa ctu rin g o f th e la bora to ry s te p ● in cre ase d r is k o f fr a ctu re d urin g th e v a rio us s te ps o f th e p ro ce ss (la bora to ry , tr y -in , a nd c e m enta tio n) d ue to th e th in ness o f th e ve neer, ● crit ic a l c e m en ta tio n p ro ce ss a n d th oughtfu l m ain te nance th era p ie s, co nce rn in g th e m ain te nan ce o f th e a esth etic r e su lt , ● These v e neers d o n ot in vo lv e th e a re a s o f d yn am ic v is ib ilit y , w hic h will b eco m e v is ib ly p re se nt w it h th e n atu ra l d ark e n in g o f th e d enta l su bstr a te . 8 Extensive preparation The to oth is a t g re ate r r is k w he n th e p ote ntia l tr e a tm en t r e q uir e s e xte nsiv e pre para tio n. B eca use th is c a n m ay to : ● Bio lo gic ir rit a tio n to th e p ulp ● Adhesio n im pa ir m ent. In th is c a se , th e p re p ara tio n is e xte nded to th e p ro xim al s u rfa ce s a nd ove rla ps th e fr e e e dge in w hat w as c o m monly r e fe rr e d to a s " p ala ta l ove rla p". ​Alt h ough th e p re para tio n is s li g h tly e xte nde d to th e li n gual s u rfa ce in cre asin g th e to ta l s u rfa ce o f e n am el fo r b ondin g, a t th e s a m e tim e a ls o cre ate s th e c o rre ct p a th fo r in se rtio n d urin g th e tr y -in a nd c e m en ta tio n, th is ty p e ​ o f v e neer p re p ara tio n c a n b e c o nsid ere d e xte nsiv e . Desp it e th e g ood b io lo g ic in te gra tio n a nd th e q ualit y o f c e m enta tio n, th e pala ta l o ve rla p le d to m ech a nic a l c o m plic a tio ns, r e la te d to a r e posit io nin g of th e p ala ta l m arg in in t h e a re a o f g re a te st fu nctio nal s tr e ss; th e c in gulu m . This ty p e o f p re para tio n , th ere fo re , h ad tw o m ajo r ​dra w backs ​: 1. Fre quent d ebond in g o f th e r e sto ra tio n d ue to fu nctio nal o ve rlo ad durin g o cclu sio n . 2. This in va siv e p re pa ra tio n r e su lt e d in e xce ssiv e d entin e xp osu re . Pala ta l c o nca vit y th a t p ro vid es th e in cis o r w it h it s s h arp in cis a l e dge a nd cu ttin g a bilit y , p ro ve d to b e a n a re a o f s tr e ss c o nce ntr a tio n. L ogic a lly , th e pre para tio n s h ould p re fe ra bly n o t fin is h a t th e c o nca vit y b ut r a th er it s h ould be p la ce d e it h er a bove th e c o nca vit y o r b elo w o n th e s m oo th c o nve x a re a of th e c in gulu m s o t h at th ey w il l b e s u bje ct to lo w te nsile fo rc e s. P la ce m ent of th e lin gual fin is h li n e fo r a la m in ate v e neer w ill a ls o d epend o n th e th ic kn ess o f th e to oth a nd t h e p atie nt's o cclu sio n. 9 10 If th e p re para tio n n e eds to b e e xte nded p ala ta lly o ve r th e in cis a l e dge, th e re m ain in g p art to w ard s th e in cis a l s h ould h ave e nough th ic kn ess to p re ve nt bre aka ge. W hen th e t e e th a re th in ner th an 1 .5 m m la bio -li n gually a t th e in cis a l th ir d , r e ducin g th e la b ia l a n d th e lin gual s u rfa ce s in cis a lly b y 0 .5 mm, th e p re para tio n le ave s u s w it h a th in s liv e r to oth s tr u ctu re th at c a nnot be r o unded o ff a nd is s u sce ptib le to b re a kin g. T hese a re as a re s o m etim es ke pt s o th in th at th e y e ve n b re ak a t th e la bora to ry w hile th e te ch nic ia n tr ie s to ta ke th e r e fr a cto ry d ie s o ut o f th e im pre ssio n, o r a t th e tim e o f th e pro vis io nal r e m ova l. T his s it u atio n m ay c a use a noth er s e rio us p ro ble m if th e tip o f th e s to ne m od el c o in cid es w it h th e v e ry th in p ortio n a nd is b ro ke n durin g th e la b p ro ce dure s, r e su lt in g in a c e ra m ic v e neer w it h e xtr a porc e la in in th at a re a . When th at v e neer is s e ate d o n th e to oth , c a re m ust b e ta ke n to a vo id mis ta ke s d ue to th e o ve rb ulk e d in te rio r s u rfa ce o f th e in cis a l e dge w hic h will m ake it im possib le to s e at th e v e neer p ro p erly a nd r e su lt in a n in accu ra te fit a t th e c e rv ic a l m arg in . The a uth ors d o n ot a dvo ca te p e rfo rm in g th is te rm in atio n b eca use th e bio lo gic a l c o st is h ig he r. T he c re atio n o f a n in se rtio n p ath fa cilit a te s th e ce m enta tio n s te p, h ow eve r p ro m ote s a h ig her v o lu m e o f w ear, p artic u la rly in th e p ro xim al r e gio n s t o e lim in ate r e te ntio n. H ence , s tr a ig ht- ty p e in cis a l 11 te rm in atio ns a re p re fe ra bly c h ose n w hen r e d uctio n is n ece ssa ry b eca use it advo ca te s a p assiv e fit in th e la b ia l- p a la ta l d ir e ctio n w it h out a d elib era te in se rtio n a xis , g re ate r p re se rv a tio n o f to oth s tr u ctu re , a nd le nds a bso lu te co nfid ence in th e b on din g m ech anis m s. 12 Conventional preparation I’d lik e to ta lk a bout a p re p ara tio n th at fo llo w s th re e m ain s ta ges a pplie d to fo ur m ain a re as o f th e to oth . Thre e m ain s ta ges ​ t o g et th e fin al v e neer p re para tio n: 1. Cuttin g 2. Refin em en t 3. Fin is h in g & p o li s h in g Four m ain a re as: 1. ​In cis al e d ge 2. ​Cerv ic al m arg in 3. ​Lab ia l/b ucc al s u rfa c e 4. ​Pro xim al s u rfa c es. Each to oth s u rfa ce ( in ca sa l, c e rv ic a l, la bia l/ b ucca l, m esia l o r d is ta l) w ill pass b y th ese s ta ges o f p re pa ra tio n. S o, le t's g et s ta rte d.. 13 Cutting An e sse ntia l q uestio n fo r t h e d enta l p ra ctit io ner; h ow to c o ntr o l y o ur h and durin g te eth p re para tio n fo r c e ra m ic v e neer? , o r in o th er w ord s, w hat is th e penetr a tio n d epth o f th e b ur t h ro ugh th e to oth s u rfa ce ? a nd T he k e yp oin t here is th e ​Dep th C utte rs . As w e a ll k n ow , th e fir s t s te p fo r th e a ctu al te eth p re para tio n is to o bta in a su ffic ie nt d epth w it h th e h elp o f d epth c u tte rs . H ow eve r, th e d epth c u tte rs alw ays r e duce th e s a m e a m ou nt o f to oth th at th eir g rid d epth in dic a te s. In oth er w ord s, n o m atte r w hat t h e p osit io n o f th e to oth is , o r w heth er th ey a re lin gually o r b ucca lly in clin ed , th e d epth c u tte r w ill a lw ays r e m ove th e s a m e am ount o f to oth s tr u ctu re t h a t w ill n ot n ece ssa ril y d ic ta te th e tr u e d epth o f th e r e sto ra tio n. F or th e in e xp erie nce d d entis t, w ho r e lig io usly fo llo w s syste m atic p re para tio n te ch niq ues fo r c e ra m ic , th e im pro per a pplic a tio n o f th ese d epth c u tte rs c a n b e e xtr e m ely d estr u ctiv e . Four e sse ntia l r u le s: ● No c e rv ic a l g ro ove ● In cis a l g ro ove 2 m m fr o m th e fr e e e dge ● 0.5 m m in th e b ucca l ( a t th e c o ro nal tw o th ir d s) ● 1.5 - 2 m m a t th e fr e e e d ge Vertic al ​Vs ​ Horiz o nta l ​ d ep th c u ts Pre para tio n o f v e stib ula r g ro ove s in th e ​ve rtic a l ​ d ir e ctio n w it h ro unded-e nded c o nic a l d ia m ond b urs , r e sp ectin g th e a xia l in clin atio ns (c e rv ic a l, m id dle a nd in cis a l) to p re se rv e th e c o nve rg ence o f th e b ucca l su rfa ce . T he d epth o f e ach g ro o ve is d efin ed a cco rd in g to e ach c a se a nd base d o n th e d ia gnostic w ax-u p. In th is w ay, o ne c a n c h eck th e a m ount o f wear w it h a m illim ete r p ro b e b y c o m pa rin g th e p re p are d s id e w it h th e in ta ct. A t th is p oin t, it is e sse ntia l to h ave k n ow le dge a bout th e th ic kn ess o f th e la bia l e nam el o f a n a tu ra l t o o th , s o th at th e c o m ple tio n o f th e pre para tio n is p erfo rm ed , h a vin g a ls o th e p re se rv a tio n o f e nam el a s 14 a g uid e w heneve r p o ssib le . T hen, jo in in g th e la bia l g ro o ve s w it h a c o nic a l dia m ond b ur, th e la rg er d ia m ete r to p re ve nt d eepenin g o f th e g uid e gro ove s a nd fo rm in g a n u n eve n s u rfa ce . Horiz o nta l ​“ d epth c u ts “ g iv in g u s m ore c o n tr o lle d c u ttin g. A s p ecia l th re e-tie r d ia m ond d e pth c u tte r c o m es in d if fe re n t th ic kn esse s 0 .3 , 0 .5 , o r 0.8 is u se d to c u t a cro ss t h e la bia l s u rfa ce th en m ark th e d epth c u ts w it h a pencil o r a m ark e r th en th e c u ttin g ​is c o m ple te d r e sp ectin g th e tr ip le angula tio n o f th e la b ia l s u rfa ce to th e b ase o f th e d epth c u ts u ntil r e ach in g th e m ark in gs. 15 The d epth c u tte r c a n o n ly p ene tr a te u ntil th e n on-c u ttin g s h aft is flu sh wit h th e to oth s u rfa ce . T he s h ap e o n th e r ig ht r e p re se nts th e s u rfa ce afte r th e d epth c u tte r is u se d a t o nly o ne a ngle . N ote th at th e o nly tr u e depth is g ain ed in th e a re a o f B ( m id dle th ir d , b la ck d ots ), to r e ach th e nece ssa ry d epth in p oin ts A ( g in giv a l th ir d , g re e n d ots ) a nd C ( in cis a l th ir d , r e d d ots ), th e b u r s h ou ld b e u se d in th re e d if fe re nt a ngula tio ns. 16 Hom ogeniz a tio n ​ o f t h e g ro ove s is d one r e sp ectin g th e b ucca l c o nve xit y . Whate ve r th e p re pa ra tio ns to b e p erfo rm ed, it is e sse ntia l th at th e m arg in s are p ro perly d efin ed ( c e rv ic a l a n d p ro xim al) s o th ey c a n b e e asily id entif ie d by th e te ch nic ia n. T his w ill a ll o w a g ood fit o f th e v e neers , b ette r s ta bilit y , and h ig her a dhesio n v a lu es. E ve n if th ere is n o n eed fo r th ic kn ess it is esse ntia l to u se a ir b orn e-p artic le a bra sio n o n th e e nam el s u rfa ce in o rd er to o ptim iz e b ondin g a n d r e m ove th e a pris m atic e nam el la ye r. The p re para tio n d esig n c o nsis ts o f th e p re p ara tio n o f d if fe re n t to oth su rfa ce s: 1. In cis a l e dge p re para tio n . 2. Cerv ic a l m arg in p re para tio n 3. Labia l/ b ucca l s u rfa ce " T rip le a n gula tio n" 4. Cre atio n o f a p ro xim al s lid e. 17 1. In cis al e d ge p re p ara tio n : There a re tw o b asic te ch n iq ue s fo r th e p la ce m en t o f th e in cis a l fin is h lin e: The fir s t te rm in ate s th e p re pare d fa cia l s u rfa ce a t th e in cis a l e dge. T here is no in cis a l r e ductio n o r p re p o f th e lin gual s u rfa ce a nd it c a n b e in th e fo rm of a w in dow o r 1. in tr a -e nam el p re para tio n o r th e fe ath ere d in cis a l p re p ara tio n. In th e s e co nd te ch niq ue , th e in cis a l e dge is s lig htly r e d uce d a nd th e porc e la in o ve rla ps 2. th e in cis a l e dge " B utt- jo in t" The ​tw o te ch niq ues w ere u se d e qu ally a nd b oth p ro vid ed c lin ic a ll y acce pta ble r e su lt s . Butt-jo in t m arg in In ste ad o f a c h am fe r m arg in th at m ay w eake n th e fin al r e sto ra tio n ( s e e Exte nsiv e p re para tio n), a f la t s h o uld er s h ould b e u se d a t th e in cis a l e dge. How eve r, if th e to oth e xh ib it s t h e le ngth d esir e d fo r th e c e ra m ic v e neers , a re ductio n w ill b e r e quir e d w hic h w ill e sta blis h a th ic kn ess o f 2 .0 m m in th e bucca l p ala ta l d ir e ctio n o f th e in cis a l m arg in . S ub se quently , a fla t in cis a l su rfa ce th at e m erg es p erp en dic u la r to th e a ngle o f th e fin al e m erg ence pro file in th e v e neers s h ould c re ate th e d elic a te in cis a l e dge c o nfig ura tio n where th e in cis a l e dg e g ro ove s a re c o nnecte d. 18 * A noth er in te re stin g d ia m ond p oin t th at I w ould lik e to u se fo r in cis a l pre para tio n is th e w heel- s h ap ed, b ut y o u h ave to b e c a re fu l w hile u sin g it to pro te ct th e n eig hbourin g s o u nd te eth . 19 20 Anoth er im porta nt a sp ect to b e a w are o f is th e c o ndit io n o f th e p ala ta l su rfa ce o f th e to oth t h at is a bo ut to b e p re p are d . T he fin is h lin e o n th e lin gual a sp ect o f th e r e sto ra tio n s h ould n ot e nd o n a w ear fa ce t a nd it is als o p re fe ra ble n ot to p la ce th e fin is h lin e o n th e c e ntr a l c o nta ct p oin ts . In th e c a se o f a w orn in cis a l e dge , a 2 m m r e d uctio n fr o m th e d esir e d le ngth of th e fin is h ed v e neer is r e q uir e d. If th e a lr e a dy e xis tin g to oth le ngth is 1 .5 mm s h orte r th an th e e xp e cte d fin al o utc o m e th en in o rd er to a ch ie ve a 2 .0 mm in cis a l r e ductio n, o nly 0 .5 m m o f p re p ara tio n w ill b e s u ffic ie nt. ** T he fr a ctu re p ote ntia l o f th e fin al r e sto ra tio n c a n b e a vo id ed b y th e ro undin g ​of th e in cis a l lin e a n gle s th at r e duce th e in te rn al s tr e ss. The b utt jo in t p re pa ra tio n is s im ple r a nd c o nsu m es le ss tim e th an th e to oth pre para tio n w it h p ala ta l c h am fe r, a nd th e m aste r c a st c a n b e u se d fo r a pre cis e p ala ta l fin is h lin e. T he p ath o f in se rtio n is fr o m th e fa cia l. T here fo re , only b utt jo in t in cis a l p re p ara tio ns w ill a llo w s u ch a b ucca l- p ala ta l p ath o f in se rtio n. Advan ta g es: ● The p orc e la in is s tr o nger a nd p ro d uce s a p osit iv e s e at d urin g th e ce m enta tio n p ro ce ss. ● The p ro per s e atin g o f t h e v e neer is m ad e p ossib le b y th e v e rtic a l s to p th at th e in cis a l o ve rla p p ro vid e s. ● The e sth etic c h ara cte ris tic s o f th e p orc e la in v e neer a re m ore e asily handle d a nd c o ntr o lle d b y t h e d enta l te ch nic ia n to im pro ve th e tr a nslu ce ncy o f th e v e ne er. ● it r e duce s s tr e ss c o nce ntr a tio n w it h in th e v e neer b y d is tr ib utin g th e occlu sa l lo ad o ve r a w id er s u rfa ce . The in cis a l in vo lv e m ent o ffe rs m any a dva nta ges a bove a ll b y th e p ossib ilit y of in co rp ora tin g in cis a l c h a ra cte riz a tio ns s u ch a s tr a nslu ce ncy, e vid ence o f th e s p in dle s, a nd o f th e o pa cit y o f th e h alo to th e r e sto ra tio ns, m im ic kin g it s natu ra lit y . 21 Win dow D esig n A w in dow d esig n p re pa re d e ntir e ly in to th e e nam el w as r e sis ta nt to a xia l str e ss. 22 Advan ta g e It is c o nsid ere d th e m ost c o n se rv a tiv e p re p ara tio n d esig n o r win dow p re para tio n is t h e t r e atm ent o f c h oic e w hen s tr e n gth is th e fir s t p rio rit y . Dis ad van ta g e It m ay r e su lt in a n a esth etic p ro ble m d ue to th e fa ct th at th e pre para tio n fin is h es in th e m ost tr a n slu ce nt a re a o f th e to oth . T his is in dic a te d in c a se s o f s u b str a te s w it h th e d esir e d v a lu e w it h out ch ro m atic a lt e ra tio n in th e in cis a l r e g io n. 23 2. G in giv al m arg in p re p ara tio n: Perip hera l d elim it a tio ns o f t h e p re p ara tio n w it h s p heric a l d ia m on d b urs su rro undin g th e e ntir e la bia l s u rfa ce o f th e to oth w it h out d is ru ptio n o f th e pro xim al c o nta ct a nd w it h out s u bgin giv a l e xte nsio n. A s p heric a l d ia m ond poin t, u se d a t a 4 5-d e gre e a ngle to th e s u rfa ce , s o th at o nly h alf th e dia m ete r o f th e p oin t p ro m ote s th e r e d uctio n. 24 NB. ​Pre para tio n o f t h e s u b gin g iv a l c e rv ic a l m arg in a nd in it ia l fin is h in g o f th e p re para tio n in in dic a te d s it u atio ns w it h r o u nded-e nded d ia m ond b urs . It is w orth e m phasiz in g th e im porta nce o f g in giv a l tis su e p ro te ctio n d urin g pre para tio n, in o rd er to p re ve nt p ost- tr a u m atic g in giv a l r e ce ssio n, esp ecia lly in th in m arg in al tis su e. 25 The fa bric a tio n o f th e c e ra m ic v e neers is d ir e ctly a ffe cte d b y th e p la ce m ent of th e fin is h in g lin e. S m oo th m arg in s th at a re fu lly e xp ose d a nd r e adily cle ansa ble g enera lly p ro vid e th e b est r e su lt s . T he d entis t h as to d ete rm in e where to p la ce th e fin is h in g lin e w here th e m arg in s o f th e r e sto ra tio n c a n be k e pt c le an b y th e p atie n t a n d p ro p erly fin is h ed. In a ddit io n, fin is h lin es must b e p la ce d s o t h at th ey c a n b e d uplic a te d b y th e im pre ssio n, w it h out te arin g o r d efo rm in g t h e im pre ssio n w hen it is r e m ove d p ast th em . Wit h n o c e m ent lin e o r m arg in v is ib le , th e p orc e la in b le nds in w it h th e underly in g c o m posit e r e sin in a h arm onio us fin is h . W heneve r p ossib le , th e fin is h lin es s h ould b e p la ce d in th e e nam el fo llo w in g th e c o nto ur o f th e s o ft tis su e fr o m m esia l- p ro xim al to d is ta l- p ro xim al. 26 Supra g in giv al M arg in : Pla ce m ent o f th e g in giv a l m arg in s u pra g in giv a lly o r c o ro nally fr e es th e gin giv a l m arg in . T his h a s m any ​ ​adva n ta ges ​ s u ch a s: 1. Elim in atin g th e c h a nce s o f in ju ry to th e g in giv a l tis su e 2. Decre asin g th e r is ks o f u nd ue e xp o su re o f th e d entin in th e c e rv ic a l re gio n 3. Obta in in g c ris p c le ar m arg in s 4. offe rin g e asie r a cce ss to th e fin is h in g a nd p olis h in g s ta ges w it h e asily acce ssib le m arg in s. 5. Im pre ssio ns a re e a sie r t o m ake . 6. Durin g th e tr y -in a n d b ond in g s ta ges, p ro p er is o la tio n o f th e o pera tiv e fie ld is e asie r, s o m ois tu re c o ntr o l a nd th e c h ance s o f c o nta m in atio n durin g a dhesiv e p ro ce dure s a re r e d uce d. 7. Posto pera tiv e ly it e lim in a te s t h e p ossib ilit y o f im pin gem en t o n bio lo gic a l w id th s b y a n in adve rte nt o ve re xte nsio n o f th e p re p ara tio n 8. Makin g it p ossib le fo r th e p a tie nt to p erfo rm m etic u lo us h yg ie ne in th is c rit ic a l r e gio n. 9. Allo w in g th e d entis t to e va lu ate m arg in al in te grit y d urin g th e fo llo w -u p and m ain te na nce v is it s . 10. In cre asin g t h e li k e lih ood th at th e r e sto ra tio n w ill e nd o n e nam el and th is in cre ase d a re a o f e nam el is e xtr e m ely im porta nt fo r s tr o nger adhesio n a nd le ss m ic ro le aka g e in th e fu tu re . Restr ic tio ns to e nam el is a n e ce ssit y fo r m arg in al to oth p re para tio ns a nd bonded r e sto ra tio ns a s e xp osu re o f th e d entin m arg in s m ay r e d uce b ond str e ngth s a nd in cre ase t h e c h ance o f m ic ro le aka ge. W hen th e p re para tio n marg in s a re c o m ple te ly lo ca te d in th e e nam el, ​mic ro le aka ge ​ is m in im al o r none a t th e to oth -lu tin g a gen t in te rfa ce a nd n eglig ib le in th e r e sin /p orc e la in in te rfa ce . It is a lw ays b ette r to fin is h th e c e rv ic a l m arg in o n e nam el s in ce more m ic ro le aka ge h as b ee n fo und a t th e lu tin g c o m po sit e /to oth in te rfa ce when th e c e rv ic a l p re para tio n m arg in w as lo ca te d in th e d entin . 27 Subgin giv al M arg in : The r e actio n o f th e g in giv a l tis su es la rg e ly d epends o n th e c e rv ic a l exte nsio n o f th e r e sto ra tio n in r e gard to th e lo ca tio n o f th e g in giv a l m arg in . Genera lly s p eakin g, th e m ajo r e tio lo gic a l fa cto r in p erio dontit is is th e su bgin giv a l p la ce m en t o f a r e sto ra tio n. In a m ajo rit y o f th e c a se s, it is b est to p la ce th e s u bgin giv a l e xte nsio n o f th e in tr a su lc u la r m arg in s a t a bou t h a lf th e w id th o f th e c re vic e d epth ; ● to c re ate a b uff e r z o ne b e tw een th e e pit h elia l a tta ch m en t a nd th e b ur, to p re ve nt e ncro ach in g o f t h e e pit h elia l a tta ch m en t o f th e b io lo gic wid th if th e p re para tio n w as e xte nded d eeper th an th e d esir e d d epth . ● to le ave e nough s p ace fo r th e g in giv a l c o rd p la ce m ent. The d eeper th e r e sto ra tio n m arg in r e sid es in th e g in giv a l s u lc u s, th e g re ate r th e c h a nce o f in fla m mato ry r e sp onse a nd th at s u ch tis su es c a n b le ed u p on p ro bin g. Dis a dva nta ge : The d if fic u lt y o f v is u ally fo ll o w in g th e c e rv ic a l m arg in s s o th at eve n th e e xp erie nce d r e sto ra tiv e d entis t c a n m is s m arg in al defe cts . Adva nta ge: It a ​llo w s th e te ch nic ia n to p re se rv e th e e xis tin g h eig ht o f th e papilla a s w ell a s to m ake c e rta in th at a ll in te rp ro xim al s p ace s and/o r d ia ste m as w il l b e c lo se d w hile p erm it tin g c o ntr o l o ve r th e em erg ence p ro file s. * n on o r m in or to oth c o lo r c h ang es ( s u ch a s o ne o r tw o s h ades lig hte r), th ere is n o n eed to p re p th e to oth s u bgin giv a lly . In o th er w ord s, o nce th e te eth a re fr e e fr o m d is co lo ra tio n o r p re se ntin g " d is cre te c o lo r a lt e ra tio n", th e g in giv a l m arg in m ust n o t b e p la ce d in th e g in giv a l s u lc u s. 28 * It is n ot o nly th e c o lo r b ut th e n atu re o f th e lip -li n e a s w ell th at d ete rm in es wheth er th e c e ra m ic v e neers m arg in al p la ce m en t w ill b e s u pra gin giv a l, equig in giv a l o r s u bgin giv a l. I f th ere is g in giv a l e xp osu re w hile s m ilin g, su bgin giv a l p la ce m en t m ay b e n ece ssa ry in o rd e r to a ch ie ve d esir a ble esth etic r e su lt s , b ut t o a c e rta in e xte nt, it d epends o n th e e sth etic exp ecta tio ns o f th e p atie nt. It is s till r e co m mend ed th at th e p la ce m en t b e s u pra g in giv a l w heneve r possib le . Cham fe r P re p ara tio n It is a lm ost im possib le to f in is h a ccu ra te ly fit tin g c e ra m ic v e neers w it h out bein g o ve rc o nto ure d o ve r a k n if e -e d ge p re p ara tio n a t th e c e rv ic a l a re a. There fo re , ir re sp ectiv e o f it s p la ce m en t ( s u b o r s u pra gin giv a lly ), a c h am fe r is p re fe rre d fo r a ll th e g in g iv a l m arg in s. ● In c o m paris o n w it h th e 9 0-d eg re e s h ould er, th e c h am fe r fin is h pre se rv e s m ore n atu ra l to oth s tr u ctu re . ● Owin g to th e g ra dua l c o lo r tr a nsit io n b etw een r e sto ra tio n a nd to oth su bstr a te , th ere by a vo id in g th e s u dden d elin eatio n b etw een to oth a nd cro w n, it is a ls o a b ette r o p tio n e sth etic a lly . ● Very d is tin ct a nd v is ib le f in is h lin e b y r e m ovin g th e s e rr a te d ove rh angin g e n am el p ris m s. To a vo id p erio donta l in fla m mato ry r e sp onse s a nd fu tu re g in giv a l r e ce ssio n, im pro vin g th e g in giv a l a rc h it e ctu re , s u rv e y lin es a nd p oin ts o f c o nca vit y wit h a c h am fe re d m arg in w hile c a re fu lly c o ntr o llin g th e a nato m ic a l c o nto urs in th e c e rv ic a l th ir d , is o f t h e u tm ost im po rta nce . T he r o u nded tip o f th e fis su re d ia m ond b ur w il l e nab le th e c e rv ic a l m arg in to b e in it ia te d s lig htly above th e g in giv a l le ve l. 29 3. T rip le a n gula tio n : To p ro vid e a n atu ra l h ealt h y lo ok fo r th e in cis o r th at m im ic s it s tr u e c o nve x natu re , a u nif o rm r e m ova l o f t h e s u bstr a te is e sse ntia l a nd c a n b e a ch ie ve d th ro ugh th e u se o f th e b ur, k e epin g it a t th re e d if fe re nt a ngle s. One o f th e m ain c h a ra cte ris tic s o f th e v e neers is b io lo gic a l p re se rv a tio n. This is p ossib le w hen th e b u cca l c o nto ur is p re se rv e d d urin g p re para tio n, by fo llo w in g th e th re e in clin atio ns o f th e n atu ra l to oth ; th e c e rv ic a l th ir d , mid dle th ir d a nd in cis a l t h ir d . S o, th e v e neer c a n b e in se rte d in a r o ta tio nal move m ent a llo w in g p re se rv a tio n o f th e e nam el a nd a cce ss to c e rv ic a l a nd pro xim al u nderc u ts a re as. It is im porta nt to n ote t h a t: * in th e v e rtic a l d im en sio n b y u sin g th re e a ngle s o f th e b ur * in th e h oriz o nta l d im en sio n b y fo llo w in g th e to oth m orp holo gy. Oth erw is e , o ne p la n e fa cia l r e du ctio n m ay c o m e to o c lo se to th e p ulp . When th e d ia m ond is s w ept in th e m esio dis ta l d ir e ctio n, a g entle c o nve x su rfa ce in th e g in giv a l a n d in cis a l 1 /3 rd s is o bta in ed. 30 31 32 Tooth p re para tio n w it h ou t r e sp ectin g th e fa cia l c o nve xit y . S uch s tr a ig ht pre para tio n c a n r e su lt in ir re ve rs ib le p ulp d am ag e. If th e in cis a l o r th e c e rv ic a l th ir d is n ot p re p are d d eeply e nough, th e fin al re sto ra tio n m ay b e o ve rc o n to ure d in th is a re a . 33 A c o m mon e rro r is t o p la ce th e in cis a l th ir d to o fa r la bia lly in th e fin al re sto ra tio n. T his is fr e qu ently d ue to in su ffic ie nt to oth r e d uctio n. T he pre para tio n m ust r e pro du ce th e n atu ra l c o nve xit y o f a m axilla ry c e ntr a l in cis o r a nd p ro vid e fo r a m in im um r e d uctio n th ic kn ess o f 0 .7 a t th e ju nctio n o f th e m id dle a nd in cis a l th ir d s o f th e to oth . In su ffic ie nt to oth re ductio n, in te rm s o f le avin g a s h arp lin e a ngle a nd n ot r o u ndin g o ff th e in cis a l la bia l a re a, is th e le ad in g c a use o f a n o ve r ta pere d p re p ara tio n o r pro duce s o paque s h ow th ro ugh, o r o ve rc o n to urin g o f th e in cis a l th ir d o f th e r e sto ra tio n. This w ill n ot o nly in flu en ce th e e xte rn a l fa cia l fo rm o f th e to oth b ut th e lig ht r e fle ctio n a s w ell. L ig ht r e fle cts o ff th e to oth a nd tr a ve ls th ro ugh it a t th e in cis a l. If th e e dge h as a r o u nded s u rfa ce a t th e in cis a l- la bia l, th at re fle cte d lig ht is b ein g d if f u se d a nd y ie ld s a n id eal tr a n sit io n o f th e s h ade fr o m th e in cis a l c o lo r t o b o dy c o lo r. 4. C re atio n o f a p ro xim al s lid e: This s ta ge is c h ara cte riz e d a s o ne o f th e m ost c o nflic tin g p oin ts d urin g pre para tio ns fo r a fix e d p ro sth esis , p erfo rm in g r e d uctio n to e nable in se rtio n a xis a nd e li m in atio n o f r e te ntio ns. It is e sse ntia l to u nders ta nd th e fa ct th at th e m ajo rit y o f c a se s o f c e ra m ic v e neers w it h o r w it h out pre para tio n, p re se nts a p assiv e fit in th e la bia l- p a la ta l d ir e ctio n, a nd th e su ppose d in te rp ro xim al r e te ntio ns a re o ve rlo oke d w hen v e neers “ fit in ” wit h out r e sis ta nce . In th is w ay, it is p ossib le to c a rry o ut m ore co nse rv a tiv e in te rp ro xim al p re pa ra tio ns, r e str ic te d m ain ly to th e c e rv ic a l re gio n e ve n if r e te ntio ns e xis t w hen v ie w ed p ra g m atic a lly in a n in cis o -c e rv ic a l s e nse . The c re atio n o f a p ro xim al s li d e a llo w s p la ce m en t o f v e neers when th e p ro xim al a nato m y is c h alle ngin g, a s w ell a s c re a tio n o f a p ro per e m erg en ce p ro file . The p re para tio n fo r th e p ro xim al s u rfa ce s m ust b e th oro ughly p la nned. T he aim m ust b e to p la ce t h e m arg in s b eyo nd th e v is ib le a re a a nd to p re se rv e th e c o nta ct a re a. E sth etic s s h ou ld b e c a re fu lly c o nsid ere d w hen p la cin g th e pro xim al " s to p-lin e", p ro vid in g t h a t th e te eth a re fr e e o f p ro xim al re sto ra tio ns. It is v e ry im porta nt to g o b eyo nd th e v is ib le a re a th at c a n b e vie w ed fr o m th e fr o nt o r s id e, e sp ecia lly w hen to oth c o lo r is v e ry d if fe re nt fr o m th at o f th e la m in a te v e neers . Destr o yin g th e c o nta ct a re as in o rd e r to c re a te th e m arg in s is u nnece ssa ry , but, in s o m e c a se s, t h e p re p ara tio n m arg in m ay b e e xte nded fu rth er in a lin gual d ir e ctio n. T he m arg in c a n b e d ra w n b ack e ve n m ore in th e lin gual dir e ctio n if th e ​natu ra l c o n ta ct a re a ​ha s a lr e ady b ee n lo st d ue to : ● a d ia ste m a ● re sto rin g a b ro ke n a ngle ● to e nco m pass a p ro xim al c o m posit e . A ta pere d d ia m ond p oin t o f s m alle r d ia m ete r is u se d to e xte nd th e m arg in s fr o m b oth th e m esia l a nd d is ta l a sp ects u ntil th ey a re o ut o f th e v is ib le a re a. Perfo rm in g th e p ro xim al p re p ara tio n w it h a d ia m on d b ur o f ​sm alle r dia m ete r. T he p ro te ctio n o f th e a dja ce nt te eth w it h a m eta l m atr ix is im pera tiv e . 35 The p ro xim al e xte nsio n o f th e p re para tio n is d ir e ctly a sso cia te d w it h th e sta tic a nd d yn am ic a re a o f v is ib ilit y a nd p re -e xis tin g r e sto ra tio ns. T he obse rv a tio n o f th e p re pa ra tio n in a s ta tic w ay, m ere ly b y la bia l, g iv e s a fa ls e im pre ssio n th at a ll v is ib le a re a s o f th e s u bstr a te w ere in clu ded in th e pre para tio n. T hus, t h e d yn am ic v ie w o f th e p re p ara tio n la te ra lly e nable s a n actu al v e rif ic a tio n o n w he th er o r n ot to p ro xim ally e xte nd th e p re para tio n. In o rd er to b e a ccu ra te a nd t o a ch ie ve th e b est r e su lt s e sth etic a lly a nd fu nctio nally , th e d entis t s h ou ld a lw ays b e a ble to v is u aliz e th e th re e-d im ensio nal fo rm . F or th e b io lo gic in te gra tio n o f la m in ate v e neers in to th e a re a, o ne s h o uld h a ve a b ette r u nders ta ndin g o f th e p la ce m ent a nd desig n o f th e p ro xim al f in is h in g lin e. 36 The ​dyn am ic v is ib ili t y a re a ​ is t h e e ntir e r e gio n o f th e n on-p re pare d to oth and w hic h r e m ain s v is ib le r e g ard le ss o f th e a ngle o f o bse rv a tio n. S ee th at, when o bse rv in g th e to oth fr o m a n o bliq ue v ie w a re a s o f u npre p are d enam el c a n b e s e en. T he p re p ara tio n o f th is a re a is e sse ntia l to th e su cce ss o f th e e sth etic s r e sto ra tio ns, e sp ecia lly in d ark e ned te eth . E ve n non-d is co lo re d te eth , h ow eve r, a ls o r e q uir e th is c a re , to e nsu re lo ng-la stin g ve neers . In th e p re pa ra tio n o f th ese r e g io ns, th e s a m e fin e a nd e xtr a -fin e grit d ia m ond p oin ts a re e m plo ye d. T he a im is to e xte nd th e p re p ara tio n until th e m arg in s a re fu lly h id den, w hate ve r th e p osit io n o f o bse rv a tio n is . Note th at w it h in th e s u bco nta ct p ro xim al a re a s it is n ece ssa ry to d is p la ce th e p re para tio n m arg in s to a c o nsid era b le e xte nt to w ard s th e p ala ta l. T o min im iz e th e c h ance s o f in adve rte ntly r e a ch in g th e p ro xim al s u rfa ce o f th e adja ce nt to oth , s tr ip s o f a m eta llic m atr ix a re r e co m m ended fo r p ro te ctio n. It is a ls o in te re stin g a t th is s ta ge to w ork w it h d ia m on d p oin ts s lig htly angle d w it h r e sp ect to th e lo ng a xis o f th e to oth s o th at o nly a s m all p art o f th e a ctiv e tip is in c o n ta ct w it h t h e to oth s tr u ctu re . 37 38 To fa cilit a te th e p la ce m ent o f in te rp ro xim al e xte nsio ns, th e m arg in o f th e p orc e la in v e neer s h ou ld b e h id den w it h in th e e m bra su re a re a. T he pro per in te rp ro xim al e xte nsio n w ill p ro vid e a ddit io nal s ta bilit y a nd re te ntio n, d ue to th e w ra paro un d e ffe ct. ** Y et, it s h ould b e c o nsid ere d th at p la cin g th e fin is h lin e in th e pro xim al c o nta ct a re a c re a te s a h ig her r is k o f ​in te rd en ta l d eca y ​, esp ecia lly w it h p atie nts w it h c o m pro m is e d d enta l h yg ie ne. A no th er fa cto r to c o nsid er in t h e p la ce m ent o f th e in te rp ro xim al m arg in s is th e siz e o f th e in te rd enta l s p ace . If th ere is a n u nsig htly g ap th at n eeds to be c lo se d, th e e xa ct p la ce m ent o f th e in te rp ro xim al m arg in w ill v a ry dependin g u pon th e s iz e o f t h e s p ace . The la rg er th e s p ace , th e fu rth er m esio lin gually o r dis to lin gually th e m arg in w ill n eed to b e e xte nded. O th erw is e , th e r e su lt a nt c o nta ct a re as w ill b e b ulk y a nd p ote ntia l fo od tr a ps. It is u se fu l to d iv id e th is s u rfa ce in to tw o r e g io ns: 1. The ​ g in giv o p ro xim al a re a ​, w hic h e xte nd s g in g iv a lly fr o m th e in te rd enta l c o n ta ct a re a 2. The ​in te rp ro xim al c o n ta ct a re a ​, w hic h is lo ca te d in th e in cis a l tw o th ir d s o f th e p ro xim al s u rfa ce . Gin giv o pro xim al P re p ara tio n Gin giv o pro xim al m arg in p re p ara tio n s h ould ​begin ​afte r ​ th e g in giv a l pre para tio n is fin is h ed. T he r o un d-e n d ta pere d fis su re d ia m ond is h eld at a n a lm ost 6 0-d e gre e a ng le , a nd fo llo w s th e g in giv a l p re p to w ard s th e pala ta l, fr o m b oth th e m esia l a nd th en th e d is ta l. 39 To ​bre ak ​ t h e c o nta ct o r ​ n ot ​? The esth etic and fu nctio na l dem ands of th e sp ecif ic to oth in vo lv e d will dete rm in e th e d esig n o f t h e p re p ara tio n o f th e p ro xim al w alls . To k e ep th e c o nta ct Under n orm al c ir c u m sta nce s, th is p re p ara tio n s h ould s to p ju st s h ort o f bre akin g th e c o nta ct. T he p ro xim al m arg in o n te eth th at a re fr e e fr o m co lo r a lt e ra tio n o r w it h s lig ht d is co lo ra tio n s h ould b e h id den b y th e pre para tio n m ade f a r e noug h in to th e c o nta ct a re a s o th at th e p ro xim al wall w ill e nd 0 .2 5 m m fa cia l to th e a ctu al c o nta ct a re a. Thro ughout th e p la ce m en t o f th e p ro xim al m arg in , th e d entis t m ust co ntin ually c h eck fo r a ny p ortio n o f d ark e n ed to oth s tr u ctu re b eyo nd th e p re para tio n th at w il l s till b e v is ib le a fte r th e r e sto ra tio n is c o m ple te , by fr e quently c h eckin g fr o m d if fe re n t v ie w poin ts . Pre fe ra bly , th e in te rp ro xim al m arg in s h ould s ta y s h ort o f th e c o nta ct a re a. Wheneve r p ossib le , it is b est to p re se rv e th e c o nta ct a re a , a s it is a n anato m ic a l fe atu re t h at is d if fic u lt to r e p ro d uce . ** In s o m e in sta nce s, th e d en tis t m ay o nly b e p re p arin g a s in gle to oth o r tw o te eth a nd m ust t h e re fo re p ay e xtr a a tte ntio n n ot to s cra tc h th e to oth next to it , w hic h w ill s ta y in ta ct. O ne o f th e w ays o f p ro te ctin g th e p ro xim al su rfa ce o f th e a dja ce n t to oth is to p la ce a m eta l m atr ix b and in b etw een. How eve r, s o m etim es, p o or p la ce m en t o f th is m eta l b and m ay in ju re th e papilla . ** ​When th e a ctu al tr e atm ent is in p ro gre ss a nd th e te eth a re n ot perio donta lly s ta ble , t h e n it b eco m es a c h alle nge to k e ep th em in ta ct a nd to pre ve nt d is p la ce m ent o f t h e t e e th b etw een th e p re p ara tio n a nd p la ce m ent se ssio ns. C onse que ntly , th e ​tr y -in ​ p ro ce dure s a re s im plif ie d a n d s a ve clin ic a l a dju stm ents o f th e c o nta ct a re a s w here th e fin e c e ra m ic s a re in tr ic a te ly p la ce d. 40 To o pen th e c o nta ct Certa in c lin ic a l c ir c u m sta nce s, s u ch a s: ● clo sin g a d ia ste m a o r c h angin g th e s h ape o r p osit io n o f a g ro up o f te eth , m ay r e q uir e s o m e s p ecif ic p re p ara tio n o f th e in te rp ro xim al are as in o rd er t o a llo w th e te ch n ic ia n g re a te r fr e e dom in a lt e ra tio n o f th e fo rm o r p osit io n. ● th e e xis te nce o f c a rie s, d efe cts o r p re e xis tin g c o m po sit e fillin gs. In su ch c a se s, it is im porta n t th at a fte r a th oro u gh e lim in atio n o f c a rio us dentin , th e w ea ke ne d r e sid ual e nam el th ic kn ess b e e va lu ate d. At tim es it m ay b e n ece ssa ry to fu ll- s li c e th ro u gh th e c o nta ct fr o m th e fa cia l to p ala ta l to o pen a d ia ste m a a n d to g iv e fr e e dom to th e d enta l te ch nic ia n. 41 If fo r s o m e r e aso n t h e p re pa ra tio n m ust fin is h o n th e p ro xim al c o nta ct a re a, in ste ad o f e xte ndin g t h e p re p ara tio n m ore p ala ta lly , w hic h w ill c a use th e lo ss o f in ta ct e nam el in t h e c o nta ct a re a , it c a n b e s tr ip ped to a ch ie ve a cle ar in te rp ro xim al m arg in . At th e r e sto ra tio n d e ntin in te rfa ce , th e c o nnectio n o f r e sin c e m ent to d entin may b e th e w eake st lin k. B ondin g c e ra m ic v e neers o nto a c o m posit e fillin g co nsid era bly in cre ase s t h e r is k o f fa ilu re . W hen th e p re para tio n m arg in is lo ca te d w it h in a n e xis tin g fill in g, n um ero u s fa ilu re s h ave b een r e porte d. T he auth ors b elie ve in th e in co rp ora tio n o f a ll th e e xis tin g c o m posit e fillin gs a nd ca rie s c a vit ie s in to th e p re p ara tio n a s m uch a s p ossib le . 42 A d ia m ond s tr ip s h o uld b e u se d to c re a te a d efin it e c le ar m arg in al e dge. Fin ally , T he d epth o f t h e in te rp ro xim al p re p ara tio n c a n b e c la ssif ie d a s sh ort, m ediu m a nd lo ng w ra ppin g ( M agne). 43 Refinement Durin g p re para tio n, ​gin giv a l d is p la ce m ent ​is a ch ie ve d b y delic a te ly in se rtin g th e b ra id ed r e tr a ctio n c o rd s in to th e s u lc u s s o as to a vo id a ny b le edin g. S upra gin giv a l p re para tio ns d o n ot n eed sp ecia l a tte ntio n. H ow eve r, if th e p re para tio n is s u bgin giv a l, it nece ssit a te s th e d is p la ce m ent o f th e g in giv a , to a vo id in ju ry . It m ay a ls o b e b en efic ia l t o u se n on-m edic a te d d efle ctio n c o rd s in ste ad o f th e m ed ic a te d o nes a s th ey m ay b e th e c a use o f a se co ndary g in giv a l r e ce ssio n. W hile d oin g t h is , th e c o ro nal pre para tio n lim it o f t h e g in giv a l c o nto ur o f th e to oth c a n b e re co rd ed, b efo re th e g in giv a l d is p la ce m ent. NB. ​ If th e d entis t w ants to b e c e rta in o f th e e xa ct p la ce m ent o f th e ce rv ic a l m arg in in o rd er n ot to m ake a d eeper p re para tio n th an th at is n ece ssa ry , h e/s h e s h ould d ra w a lin e a t th e p re se nt lo ca tio n o f th e g in giv a l c a vo -s u rfa ce m arg in w it h a s h arp ened pencil o r a w ate r-in so lu ble p en b efo re p la cin g th e tis su e dis p la ce m ent c o rd s in to th e s u lc u s. At th is tim e, w e s ta rt to r e fin e a ll th e p re para tio n s u rfa ce s u sin g dia m ond p ​oin ts s im ila r t o th ose m entio n ed a bove a lr e ady em plo ye d e xce pt w it h fin e a nd e xtr a -fin e g rit s . 44 Finishing and polishing A facial reduction of 0.5 mm with chamfered margins and 1.5-2 mm of incisal reduction are preferable considering the conservative nature of porcelain laminate veneers preparation. It is not difficult to ensure adequate uniform thickness that is necessary for structural integrity when under stress when there is an emphasis on conservative tooth reduction in this preparation phase. Higher stress at the surface and interface of the restoration may occur when the restoration is too thin or has a poor internal fit. Using abrasive silicone rubbers and discs with decreasing granulation. Every angle and corner should be uniform, with rounded lines, to improve the adaptation of the resin cement and laboratory build-up. One of the most important tasks is the manual instrumentation of the cervical margins. Often even after finishing and polishing, the region has small irregularities and sharp angles, related to the angle of enamel rods and the form of diamond points used for preparation. To eliminate these irregularities, the best alternative is using a manual cutting instrument. 45 46 47 48 Guided preparation A m ajo r c h ange in th e r e d uctio n p rin cip le a ppeare d in th e e arly 2 000s. There w as a s te p b ack f r o m a n in va siv e p re p ara tio n to a m ore c o nse rv a tiv e re ductio n in o rd er to o bta in s u re ly e nam ele d p re p ara tio ns. T he r e tu rn to a n enam el fin is h m in im iz e d th e r is k o f fa ilu re . This m odif ic a tio n o f th e r e du ctio n p rin cip le fo llo w s th e b io m im etic co nce pts a dvo ca te d b y M agne : “ T he u se o f a m ock-u p a s p art o f e sth etic pla nnin g, w here p re p ara tio n is g uid ed b y th e fu tu re a nd n ot b y th e p re se nt, su pporte d th is a ppro a ch a nd v a lid ate d th is n ew a ppro ach .” One of th e ve ry cru cia l is su es in th e pro ductio n of ce ra m ic ve ne ers is to ke ep th e maxim um exis tin g enam el of th e to oth str u ctu re . ​In ord er to pre se rv e th e maxim um am oun t of to oth enam el, th e fin al to oth re ductio n sh ould be desig ned acco rd in g to th e exp ecte d fin al outc o m e "g uid ed pre p". If not, th e re ductio n of de nta l str u ctu re s will not be th e sa m e wit h in th e sp ace r e quir e m ents fo r c e ra m ic v e neers . The pre para tio n desig n fo r ce ra m ic ve nee rs sh o uld all o w fo r an optim al marg in al adapta tio n of th e defin it iv e re sto ra tio ns an d maxim ally re se m blin g th e id eal to oth morp holo gy. There fo re , a dia g nostic ​wax-u p sh ou ld be utiliz e d as a re fe re nce fo r to oth re ductio n. ​The sp atia l orie nta tio n and arc h it e ctu ra l dim ensio ns of th e wax-u p will be use d to pre -d e sig n and va lid ate th e in te nded pre para tio ns fo r th e te eth in vo lv e d. This illu str a te s th e im porta nce of usin g co rr e ct wax-u p te ch niq ues in cre atin g th e exa ct to oth sh ape desir e d. In su ch a tr e atm ent th e most im porta nt ele m en t in th e pro ce ss is th e wax-u p. In ord er to tr a nsfe r th ese data to th e clin ic , th e dentis t sh ould be su pp lie d wit h tr a nsp are nt te m pla te s and silic o n in d exe s fa bric a te d upon th e wax-u p by th e la bo ra to ry te ch nic ia n, alt h ou gh th ese in dexe s c a n b e e asily m ade a t th e c lin ic b y th e d entis t/a ssis ta nt. 49 Contr o l of re ductio n ca n be ach ie ve d by usin g ( ​pre para tio n guid es ​). Silic o ne guid es, fa bric a te d ove r th e wax-u p, pro vid e sim ple and in dis p ensa ble to ols fo r th e co ntr o l and re d uctio n of ena m el. Tw o guid es sh ould be fa bric a te d: a ​ve rtic a l ​gu id e (s e ctio ned in th e bucco lin gu al dir e ctio n) fo r re ductio n co n tr o l in ce rv ic o -in cis a l dir e ctio n; and a horiz o nta l guid e fo r th e mesio dis ta l re d uctio n co ntr o l. Usin g th e ve rtic a l and horiz o nta l silic o ne g uid es, it is p ossib le to c h eck th e u nif o rm it y o f th e la bia l r e ductio n. Guid ed p re para tio n m eans th at th e s a m e c o nsid era tio ns o f th e co nve ntio nal p re para tio n ​ a re g oin g to b e im ple m ente d b ut th ro u gh th e mock-u p ​. T he a m oun t o f to oth r e ductio n s h ould n eve r b e m ad e a cco rd in g to th e e xis tin g to oth s u rfa ce b ut r a th er to th e fin al v o lu m e o f th e r e sto ra tio n. 50 Thanks to th e te ch niq ue o f ​Gali p G üre l ​, p ro po se d a lm ost 2 0 y e a rs a go. It is a s im ple te ch niq ue, w hic h h as g re at v a lu e fo r c o ntr o llin g th e d epth o